We hypothesize that the local venule vasculature underlies the BOLD signal latency and its variability. This hypothesis was tested by measuring the BOLD signal in the human primary visual cortex with a 10-Hz sampling rate during a visuomotor and a breath-holding (BH) task. A venule probability (VP) map was estimated by susceptibility-weighted images. We found that VP was significantly correlated to the relative BOLD latency and relative latency variability during the visuomotor task. These correlations disappeared after subtracting the latency in the BH task from the latency in the visuomotor task. These results support our hypothesis.